The tracheobronchial (TB) epithelium is frequently injured by toxic air contaminants causing disturbances in cell differentiation and cell death. We are investigating mechanisms regulating regeneration in an in vitro epithelial differentiation model. I. Airway secretions. Airway secretions contain mucins and nonmucins, e.g., lysozyme (LZ), lactoferrin (LP) and the antileukoprotease SLPI. Retinoic acid (RA) was found to upregulate the mucin genes, MUC2 and MUC5, and the LZ gene, but to downregulate LF and SLPI expression. EGF and RA were found to have antagonistic effects on mucous differentiation. EGF, in the absence of RA induced squamous differentiation and suppressed mucin gene expression. RA inhibited the EGF effect and reestablished mucous differentiation and MUC2 and MUC5 expression. Experiments are underway to elucidate the molecular mechanisms by which RA inhibits the EGF effect. II. Ciliated cell differentiation. Ciliated cells are readily damaged by a variety of air contaminants. We are studying mechanisms controlling ciliated cell differentiation. We identified and cloned partial cDNAs of 7 axonemal dyneins, the biochemical motors of ciliary movement. We have cloned 5kb of the 5' end of axonemal dynein B to identify promotor regions of dynein B. Two novel genes, KPL1 and KPL2, which are upregulated during ciliagenesis were identified by differential display. These findings will help to elucidate mechanisms involved in ciliated cell differentiation.